Communication apparatus enabling temporal coexistence of systems

ABSTRACT

A coexistence controller which performs management and control of time division for coexistence, is provided in a power line communication modem which has a function as a QoS controller for a QoS type communication system and a power line communication modem for a best-effort type communication system. In the QoS type communication system, by controlling allocation of a communication band in accordance with priorities given to the communication systems by cooperation of the coexistence controller and the QoS controller, the power line communication systems having different schemes can coexist.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a communication apparatus which enablestemporal coexistence of systems, and more particularly to, acommunication system which enables coexistence of a plurality ofdifferent communication schemes (a communication system which guaranteesQuality of Service (QoS) and a communication system which performsbest-effort communication) on the same communication medium, such as apower line or the like.

2. Description of the Background Art

Power Line Communications (PLC) has attracted attention as a technologyfor connection of a network apparatus, such as a broadband router or thelike, so as to access from a Personal Computer (PC) or the like in ahome to the Internet. In the power line communication, since an existingpower line is used as a communication medium, it is not necessary toconstruct a new infrastructure, and high-speed communication can beachieved only by inserting a power supply plug into a power supplyoutlet in a home. Therefore, research and development, and demonstrationexperiments have been vigorously conducted all over the world, and inEurope and the USA, and a number of PLC projects have already beencommercialized.

An example of the PLC is HomePlug Ver. 1.0, which is a specificationcreated by the HomePlug Powerline Alliance (USA). The specification isintended to be used mainly in applications, such as the Internet,mailing and file transfer which are performed by a PC. HomePlug employsa CSMA/CA technique for a medium access control of which power linecommunication modem accesses a power line. Therefore, only best-effortcommunication which does not guarantee a band to be used can beachieved. See, for example, Yu-Ju Lin, Haniph A. Latchman, and RichardE, “A Comparative Performance Study of Wireless and Power LineNetworks”, IEEE Communications Magazine, April 2003, pp. 54-63.

FIG. 17 is a diagram illustrating a general configuration when a PC isused to access from a home to the Internet.

A PC 1101 which is used by a user is connected via an Ethernet 1102 toan Internet access router 1104, through which the PC 1101 is connectedvia an access line 1103 to the Internet 1105. As the access line 1103,ADSL (Asymmetric Digital Subscriber Line), FTTH (Fiber To The Home) orthe like is generally used. Here, it is often that a place where theaccess line 1103 is withdrawn into the home is different from a roomwhere the PC 1101 is placed. In this case, a cable of the Ethernet 1102needs to be extended from the Internet access router 1104 to the PC1101.

In the field of power line communication, in order to reduce theextension, a conversion adaptor (hereinafter referred to as a P/Econversion adaptor) between power line and Ethernet has beencommercialized. FIG. 18 illustrates a general configuration related toaccess to the Internet when the P/E conversion adaptor is used.

A PC 1101 which is used by a user is connected via an Ethernet 1102 to aP/E conversion adaptor 1205, through which the PC 1101 is connected viaan outlet to an in-home power line 1208. Data is transferred to a P/Econversion adaptor 1205 for an Internet access router 1104 by power linecommunication. The P/E conversion adaptor 1205 is connected via theEthernet 1102 to the Internet access router 1104. The Internet accessrouter 1104 is connected via an access line 1103 to the Internet 1105.

On the other hand, there is a trend toward construction of a new networkappliance system by applying Internet technologies grown in the PC fieldto AV apparatuses and communication apparatuses. The trend is beingdeveloped into a new system, such as association of an AV server (a DVDrecorder, an HDD recorder, etc.) with a TV which are placed in differentrooms (a network function is added to the AV apparatuses) , fusion of anIP telephone or an IP camera with a TV or a PC (the Internet technologyis applied).

FIG. 19 is a diagram illustrating a specific example of theabove-described new system. Communication of AV streams or speechrequires guarantee of real-time communication, unlike the conventionalInternet, mailing and file transfer. Particularly, telephone services orthe like, which perform real-time two-way speech communication, have astrict requirement for limitation on delay in communication, andgenerally, the delay is limited to about 10 msec. For such servicesrequiring guarantee of QoS, best-effort communication does not satisfyrequired quality.

Therefore, a power line communication scheme which guarantees QoS hasbeen developed. See, for example, Shinichiro Ohmi, “A Media AccessControl Method for High-Speed Power Line Communication System Modems”,IEEE CCNC 2004. FIG. 20 is a diagram illustrating power linecommunication which performs best-effort communication (hereinafterreferred to as best-effort type power line communication) and power linecommunication which requires guarantee of QoS (hereinafter referred toas QoS type power line communication). In FIG. 20, the vertical axisindicates frequency and the horizontal axis indicates time.

In the case of HomePlug Ver. 1.0, which is one kind of best-effort typepower line communication, frequencies used therein are about 2 MHz to 21MHz. The time axis varies, depending on data generating timing or a dataamount. For displaying of a website on the Internet or acquisition of amail, the services can still hold despite their delayed arrival if thedelay is within a tolerable range.

On the other hand, many kinds of QoS type power line communication aimhigh-speed transmission of video data, and therefore, use a broaderfrequency band. Also, in order to guarantee QoS, a QoS controller isprovided in a system. The QoS controller transmits a beacon in constantintervals to control transmission timing and a transmitted data amountof a power line modem ((b) of FIG. 20). The QoS controller may beprovided as a function of the power line modem, and in the example ofFIG. 19, is included in a P/E conversion adaptor 1309.

If the amount of video data is assumed to be constant and thecommunication rate is also assumed to be constant, data having aconstant duration is transmitted on a power line in constant intervals((b) of FIG. 20). If these pieces of data do not arrive by respectivepredetermined times, video is disturbed, so that the service does nothold. In addition, an apparatus connected to the power line and itsoperating state vary with time, so that the communication state isactually not constant and varies with time. If the communication ratedecreases, a time required to communicate the same amount of datachanges. Therefore, when the power line modem which communicates videodata detects a reduction in the rate, the power line modem informs theQoS controller of that using a communication command so that a timerequired to communicate the same amount of data is allocated, therebymaking it possible to guarantee QoS. This is illustrated in FIG. 21. InFIG. 21, the power line modem which has detected a decrease in thecommunication rate transmits an allocated time change command to the QoScontroller to change a time required to communicate the following datainto a long time. Thereby, it is possible to continue to maintaincommunicating the same amount of data per unit time.

As described above, various power line communication techniques havebeen developed. However, since all power lines provided in a home areconnected to a distribution switchboard, when power line modemsemploying different communication schemes are used in the same home, asignal which is transmitted to a power line by a power line modememploying one communication scheme is noise for a power line modememploying another communication scheme. Therefore, when power linemodems employing different communication schemes perform communicationssimultaneously, the communications interfere with each other or all thecommunications are disabled as illustrated in (c) of FIG. 20, resultingin a significant reduction in communication rate.

To avoid this, for example, Japanese Patent Laid-Open Publication No.2002-368831 proposes a method for controlling data transmission of eachpower line modem when a plurality of power line modems having differentdata communication schemes are present on the same power line. FIG. 22is a diagram for explaining this conventional technique.

In FIG. 22, for example, it is assumed that a selector 61 provided in amanagement processor 6 selects power line modems 4 a to 4 m employing ascheme B as transmission-permitted power line modems. In this case, amessage generator 62 generates a transmission-permitting message whichindicates permission of transmission to the power line modems 4 a to 4 memploying the scheme B, and a transmission-forbidding message whichindicates forbiddance of transmission to power line modems 3 a to 3 memploying a scheme A. Thereafter, a power line modem 3 n employing thescheme A transmits the transmission-forbidding message to the power linemodems 3 a to 3 m employing the scheme A, and a power line modem 4 nemploying the scheme B transmits the transmission-permitting message tothe power line modems 4 a to 4 m employing the scheme B.

However, the above-described conventional apparatus for managing datacommunication apparatuses does not have means for correctly determininghow much communication time is provided to a QoS type power linecommunication system and with what timing the communication time isprovided to the system so as to enable guarantee of QoS. Also, the datacommunication apparatus managing apparatus does not have means withwhich a QoS controller of a QoS type power line communication systemdetermines how much time is provided to another power line communicationsystem. Therefore, the QoS controller does not determine how much timecan be provided to a power line modem of a system to which the QoScontroller belongs, and therefore, cannot determine whether or not arequest for a service can be accepted. Therefore, it is not possible toachieve coexistence of a QoS type power line communication system and abest-effort type power line communication system.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to provide acommunication system which enables coexistence of a QoS type power linecommunication system and a best-effort type power line communicationsystem.

The present invention is directed to, in a system in which a pluralityof communication systems coexist on the same communication medium due totime division communication, a communication apparatus belonging to acommunication system A having a high priority and a communicationapparatus belonging to a communication system B not having a highestpriority. The communication medium used by the communication systems Aand B may be a power line or a wireless medium.

To achieve the object, the communication apparatus belonging to thecommunication system A of the present invention comprises a QoScontroller for guaranteeing QoS of the communication system A, a mastercommunication manager for collectively managing transmission times ofdata communication performed by all communication modems in a pluralityof communication systems in cooperation with the QoS controller, acommand generator for generating a communication permitting commandwhich permits data communication, in accordance with an instruction ofthe master communication manager, and a transmitter for transmitting thecommunication permitting command generated by the command generator to acommunication apparatus belonging to another communication system.

Preferably, the command generator generates an active-state commandwhich informs the communication apparatus belonging to the othercommunication system of an active state of the communication system A,in constant time intervals. The transmitter transmits the active-statecommand to the communication apparatus belonging to the othercommunication system.

The communication apparatus belonging to the communication system Afurther comprises a receiver for receiving an active-state command whichinforms an active state of the other communication system, theactive-state command being generated by the communication apparatusbelonging to the other communication system. When the active-statecommand of the other communication system is received, the mastercommunication manager manages the other communication system as a targetto which the communication permitting command is to be transmitted, andwhen the active-state command of the other communication system is notreceived for a constant time or more, the master communication managerremoves the other communication system from the target to which thecommunication permitting command is to be transmitted.

Also, to achieve the object, the communication apparatus belonging tothe communication system B of the present invention comprises a receiverfor receiving a communication permitting command which is transmittedfrom the communication apparatus belonging to the communication system Ahaving the highest priority and permits data communication, and a slavecommunication manager for managing execution of data communication in aconstant time defined by the communication permitting command.

Preferably, the receiver receives an active-state command which informsan active state of the communication system A, from the communicationapparatus belonging to the communication system A. When the active-statecommand of the communication system A is received, the slavecommunication manager goes to a slave operating state, and when theactive-state command of the communication system A is not received for aconstant time or more, the slave communication manager cancels the slaveoperating state.

Preferably, the communication apparatus belonging to the communicationsystem B further comprises a command generator for generating anactive-state command which informs the communication apparatus belongingto the communication system A of an active state of the communicationsystem B, in constant time intervals, and a transmitter for transmittingthe active-state command to the communication apparatus belonging to thecommunication system A.

Note that the communication apparatus belonging to the communicationsystem A may comprise a QoS controller for guaranteeing QoS of thecommunication system A, a master communication manager for collectivelymanaging transmission times of data communication performed by allcommunication modems in a plurality of communication systems incooperation with the QoS controller, a command generator for generatinga communication slot request command which requests use of acommunication slot, in accordance with an instruction of the mastercommunication manager, and a transmitter for transmitting thecommunication slot request command generated by the command generator asa request having a high priority to a communication apparatus belongingto another communication system.

In the case of this configuration, desirably, the communicationapparatus belonging to the communication system A further comprises astate information generator for generating information about thecommunication slot used for data communication, the information being tobe transmitted via the transmitter to the communication apparatusbelonging to the other communication system, a receiver for receivingthe information about the communication slot used for data communicationfrom the communication apparatus belonging to the other communicationsystem, and a state information interpreter for interpreting theinformation about the communication slot used for data communication,the information being received by the receiver.

Preferably, the master communication manager may confirm freecommunication slots freed by the other communication system based on theinformation interpreted by the state information interpreter, and maydetermine use of a communication slot required for the communicationsystem A among the free communication slots. Note that, preferably, whenthe receiver receives the communication slot request command having ahigh priority, the master communication manager frees half ofcommunication slots which have been so far used.

Similarly, the communication apparatus belonging to the communicationsystem B comprises a receiver for receiving a communication slot requestcommand which is transmitted from the communication apparatus belongingto the communication system A having the highest priority and requestsuse of a communication slot, and a slave communication manager forperforming a control to free a communication slot which has been so farused, in accordance with the communication slot request command.

In the case of this configuration, desirably, the communicationapparatus belonging to the communication system B, further comprises astate information generator for generating information about thecommunication slot used for data communication, the information being tobe transmitted via a transmitter to the communication apparatusbelonging to the communication system A, a receiver for receiving theinformation about the communication slot used for data communicationfrom the communication apparatus belonging to the communication systemA, and a state information interpreter for interpreting the informationabout the communication slot used for data communication, theinformation being received by the receiver.

Preferably, the master communication manager frees a communication slotwhich has been so far used, in accordance with the communication slotrequest command transmitted from the communication apparatus belongingto the communication system A, confirms a free communication slot basedon information about a communication slot used for data communication,the information being to be transmitted from a communication apparatusbelonging to another communication system after a predetermined constanttime has elapsed, and use the free communication slot for communication.

According to the present invention, a QoS type communication system anda best-effort type communication system can coexist in accordance withpriorities given to the respective communication systems. Thereby, whena plurality of power line communication modems having differentcommunication schemes are introduced into a user's home, it is possibleto select which communication scheme type of power line communicationmodem is caused to manage communication. In addition, it is possible toprevent overlapping of master functions, and select which power linecommunication modem has a service which should be given priority, foreach user. Also, even when either the master or the slave becomesinactive, it is possible to achieve coexistence in which a power linecan be used with high efficiency, avoiding waste.

These and other objects, features, aspects and advantages of the presentinvention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a configuration of a power linecommunication system according to a first embodiment of the presentinvention;

FIG. 2 is a diagram illustrating an exemplary definition of a signal anda command which are received by coexistence controllers 104 and 204;

FIG. 3A is a flowchart illustrating an operation of the mastercoexistence controller 104;

FIG. 3B is a flowchart illustrating an operation of the slavecoexistence controller 204;

FIG. 4 is a timing chart based on operations of the coexistencecontrollers 104 and 204;

FIG. 5 is a flowchart illustrating another operation of the slavecoexistence controller 204;

FIGS. 6 and 7 are timing charts based on other operations of thecoexistence controllers 104 and 204;

FIGS. 8A and 8B are flowcharts illustrating another operation of themaster coexistence controller 104;

FIG. 9 is a timing chart based on other operations of the coexistencecontrollers 104 and 204;

FIG. 10 is a diagram illustrating a configuration of another power linecommunication system according to a first embodiment of the presentinvention;

FIGS. 11 and 12 are timing charts based on an operation of the otherpower line communication system of FIG. 10;

FIG. 13 is a diagram illustrating a configuration of a power linecommunication system according to a second embodiment of the presentinvention;

FIG. 14 is a diagram illustrating an exemplary definition of a signaland a command transmitted and received by coexistence controllers 304and 404;

FIGS. 15 and 16 are flowcharts illustrating operations of thecoexistence controllers 304 and 404;

FIGS. 17 to 19 are diagrams illustrating an exemplary configuration of aconventional system when the Internet is accessed from a PC in a home;

FIG. 20 is a diagram illustrating an exemplary data stream transmittedon a communication medium;

FIG. 21 is a diagram illustrating an exemplary QoS data streamtransmitted on a communication medium; and

FIG. 22 is a diagram illustrating an exemplary configuration of aconventional communication system which enables coexistence of aplurality of power line modems.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An object of the present invention is to enable coexistence of a QoStype communication system and a best-effort type communication system.The QoS type communication system includes at least one QoS controller,and causes a communication modem which provides a service to report acommunication band and a delay time required for the service. At thesame time, the QoS type communication system causes the communicationmodem which provides the service to report a communication rate varyingwith time. Based on the reported communication band and delay timerequired for the service, it is determined whether or not a newlyrequested service can be provided simultaneously with thealready-provided service, to accept or reject the request (admissioncontrol).

It is necessary to guarantee the QoS of a service whose request isaccepted, during a period of time for which the service is required.Therefore, the QoS controller allocates a constant time within a cycletime of a system for a communication modem which provides a service foreach accepted service, and indicates transmission timing to thecommunication modem. The QoS controller also has a function of acommunication modem, so that the reporting, acceptance/rejection of arequest, and instruction of transmission timing are achieved bycommunicating a communication control command defined betweencommunication modems- When a QoS type communication system needs tocoexist with another communication system, the acceptance of a requestfor a service is determined after a time used by the other coexistingcommunication system is subtracted. When a service provided by the othercommunication system is a best-effort service, a time required toguarantee QoS is secured, and thereafter, a remaining time is given tothe other communication system.

Hereinafter, embodiments of the present invention will be described,where the present invention is applied to a power line communicationsystem in which a power line is used as a communication medium. Notethat the communication medium may be a wireless medium, or a wiredmedium in addition to a power line.

First Embodiment

FIG. 1 is a diagram illustrating a configuration of a power linecommunication system according to a first embodiment of the presentinvention. In the power line communication system of the firstembodiment, a QoS type communication system A and a best-effort typecommunication system B are connected to each other via a power line. Inthis example, the communication system A is a master and thecommunication system B is a slave.

The communication system A comprises a power line communication controlmodem 101 including a power line communication modem 102, a QoScontroller 103 and a coexistence controller 104, and a plurality ofpower line communication modems 102. The coexistence controller 104performs various communications so as to achieve a control ofcoexistence with other power line communication systems. The coexistencecontroller 104 comprises a priority setter 105, a master/slavecommunication manager 106, a command interpreter 107, a commandgenerator 108, a receiver 109, and a transmitter 110. In this example,in the priority setter 105, the priority rank of the communicationsystem A is previously set to be in the first place.

The communication system B comprises a power line communication controlmodem 201 including a power line communication modem 202 and acoexistence controller 204, and a plurality of power line communicationmodems 202. The coexistence controller 204 performs variouscommunications so as to achieve a control of coexistence with otherpower line communication systems. The coexistence controller 204comprises a priority setter 205, a master/slave communication manager106, a command interpreter 107, a command generator 108, a receiver 109,and a transmitter 110. In this example, in the priority setter 205, thepriority rank of the communication system B is previously set to be inthe second place.

FIG. 2 is a diagram illustrating an exemplary definition of a signal anda command which are received by the coexistence controllers 104 and 204.For the coexistence controllers 104 and 204, an inexpensive practiceprice and high communication precision on a power line having harshcommunication conditions are required. Therefore, in the presentinvention, the case where coexistence signals transmitted and receivedbetween communication systems are synchronized with each other with highprecision using a zero-crossing point of AC mains as a time slotreference, will be described as an example.

In the present invention, a coexistence signal is used in which a firstconstant time is a slot H1 and the next constant time is a slot H2,where a zero-crossing point of AC mains is used as a reference.Combinations of bits set in the slots H1 and H2 define the followingfour control commands. Note that these control commands are only forillustrative purposes, and can be arbitrarily set in other ways.

[H1, H2]=[0, 0]: no change

-   -   [0, 1]: slave activated state (SOT: start of transmission)    -   [1, 0]: master activated state (SOT)    -   [1, 1]: transmission is permitted (EOT: end of transmission)

Hereinafter, coexistence controls performed by the coexistencecontrollers 104 and 204 will be classified and successively describedwith reference to FIGS. 3A to 9. FIGS. 3A, 8A and 8B are flowchartsillustrating an operation of the master coexistence controller 104. FIG.3B and 5 are flowcharts illustrating an operation of the slavecoexistence controller 204. FIGS. 4, 6, 7 and 9 are timing charts basedon the operations of the coexistence controllers 104 and 204.

(1) When both a master and a slave are activated

Initially, the master coexistence controller 104 having the firstpriority instructs the QoS controller 103 to start communication (stepS301). The QoS controller 103 stores a time schedule of communicationinto a beacon, taking into consideration a predetermined slot time Nmwhich is employed by the master for communication and a predeterminedslot time Ns which is employed by the slave for communication, andinforms the power line communication modems 102 belonging to thecommunication system A of the communication time schedule. Note that, ifthe sum of the slot time Nm and the slot time Ns is equal to a beaconcycle, the slot time Nm and the slot time Ns may be invariably assignedto fixed positions in the beacon cycle. Each power line communicationmodem 102 performs communication in accordance with the time schedulestored in the beacon.

After the slot time Nm has elapsed (step S302), the coexistencecontroller 104 suspends communication and issues EOT (steps S303 andS304, {circle around (1)} in FIG. 4). This EOT is generated by thecommand generator 108, and is transmitted from the transmitter 110 withtiming of a zero-crossing point and with a frequency different from afrequency for data communication. Note that it is preferable that EOT beissued one slot before the end of transmission. After the slot time Nshas elapsed since transmission of EOT (step S305), the coexistencecontroller 104 determines whether to end or continue communication (stepS306).

On the other hand, the slave coexistence controller 204 having thesecond priority goes to a state in which the slave coexistencecontroller 204 can receive a command from the master (step S311). Whenthe slave coexistence controller 204 receives EOT from the master (stepS312), the coexistence controller 204 instructs the QoS controller 203to start communication (step S313, ({circle around (2)} in FIG. 4).After the slot time Ns has elapsed (step S314), the coexistencecontroller 204 suspends communication and determines whether to end orcontinue the subsequent communication (steps S315 and S316, {circlearound (4)} in FIG. 4).

(2) When the slave is activated while the master is not activated

Upon activation, the slave coexistence controller 204 also transmits SOTconsecutively X times so as to prevent other communication systems fromfailing to receive the SOT (step S501, {circle around (1)} in FIG. 6).For example, X is generally assumed to be about eight. The coexistencecontroller 204 determines whether or not any command has been receivedfrom the master (steps S311, S312 and S502). In this case, since notransmission is performed by the master, the coexistence controller 204determines that there is no event. The number of consecutive times ofdetermining that there is no event is counted (step S506). When thecount value exceeds a predetermined number Xc, it is determined that themaster is inactive (step S507), so that free communication of the slaveis started (step S508, {circle around (2)} in FIG. 6).

(3) When the slave is activated while the master has already beenactivated

Upon activation, the slave coexistence controller 204 transmits SOTconsecutively X times (step S501, {circle around (1)} in FIG. 7). Thecoexistence controller 204 determines whether or not any command hasbeen received from the master (steps S311, S312 and S502). In this case,since SOT which is being communicated is received from the master, thecoexistence controller 204 determines that the master is active, andsuspends communication (steps S502 and S503). In this case, the countvalue of the number of consecutive times of determining that there is noevent is reset. Thereafter, the slave coexistence controller 204confirms reception of an EOT command from the master ({circle around(3)} in FIG. 7), and starts communication (steps S311 and S312, {circlearound (4)} in FIG. 7).

(4) When the master is activated while the slave has already beenactivated

Upon activation, the master coexistence controller 104 transmits SOTconsecutively X times (step S801, {circle around (1)} in FIG. 9). Theslave coexistence controller 204 itself returns SOT in response to SOTreceived from the master. In this case, the coexistence controller 204determines that the master is active, and suspends communication whichhas been so far executed (steps S502 and S503, {circle around (2)} inFIG. 9). The coexistence controller 204 continues to return SOT untilthe end of reception of SOT (step S504, {circle around (3)} in FIG. 9),and one slot after the end of the SOT reception, transmits SOTconsecutively X times ({circle around (4)} in FIG. 9).

The coexistence controller 104 determines whether or not SOT has beenreceived from the slave (step S802). In this case, since the coexistencecontroller 104 receives SOT from the slave, the slot time Nm and theslot time Ns are set to initial values Nm0 and Ns0, respectively (stepS803), and a communication process similar to that of (1) is performed.

(5) When the master is activated while the slave is not activated

Upon activation, the master coexistence controller 104 transmits SOTconsecutively X times (step S801). Thereafter, the coexistencecontroller 104 determines whether or not SOT has been received from theslave (step S802). In this case, since the coexistence controller 104does not receive SOT from the slave, the slot time Ns is set to be zeroand the slot time Nm is set to be Nm0+Ns0 (step S804), and acommunication process similar to that of (1) is performed. In this case,a counter Nno for counting the number of consecutive slots in which SOTis not received and a counter Nsot which is used by the master toregularly transmit SOT, are each incremented by the slot time Nm. Withthis process, all communication times are used by the master, therebymaking it possible to prevent from allocating slots to the slave whenthe slave is inactive.

Thereafter, the coexistence controller 104 determines whether or not thecounter Nsot which is used by the master to regularly transmit SOT hasreached a predetermined slot number Na (step S806), and when thepredetermined slot number Na is reached, transmits SOT and resets thecounter Nsot (step S807). In addition, the coexistence controller 104determines whether or not the counter Nno for counting the number ofconsecutive slots in which SOT is not received has reached apredetermined slot number Nc (step S808), and when SOT has not beenreceived before the predetermined slot number Nc is exceeded, it isdetermined that the slave is inactive, Nm, Ns and Nno are set to beNm0+Ns0, 0 and 0, respectively (step S809). With this process, allcommunication times can be used by the master without transmitting EOTuntil the subsequent SOT is received from the slave.

As described above, according to the power line communication system ofthe first embodiment of the present invention, when the coexistencecontroller and the QoS controller cooperate, the QoS type communicationsystem and the best-effort type communication system can coexist inaccordance with priorities given to the respective communicationsystems. Thereby, when a plurality of power line communication modemsare introduced into a user's home, it is possible to select which powerline communication modem is caused to manage communication. In addition,it is possible to prevent overlapping of master functions, and selectwhich power line communication modem has a service which should be givenpriority, for each user. Also, even when either the master or the slavebecomes inactive, it is possible to achieve coexistence in which a powerline can be used with high efficiency, avoiding waste.

When the QoS type communication system is given the first priority, atime or timing required to guarantee QoS can be allocated for the QoStype communication system, and a remaining time is allocated for thebest-effort type communication system. Also, a transmission right of thebest-effort type communication system can be controlled by a QoS typecommunication modem. Also, the transmission right is returned to the QoStype communication modem is invariably returned a predetermined constanttime after the best-effort type communication system startstransmission. Therefore, a variation with time in communication state ofa power line can be smoothed out by the QoS type communication systemitself adjusting a time interval allocated for a best-effort power linemodem, thereby making it possible to certainly guarantee QoS of a modemfor which QoS is required. Also, even when a time allocated for a powerline modem and a maximum value of the time interval are previouslydetermined, an admission control can be easily determined aftersubtracting a band to be allocated which is calculated from those,thereby making it possible to achieve a suitable admission control in acoexistence state.

In the above description, the case where there are two priorities of amaster and a slave has been described. If the types of commands areincreased, the present invention can be similarly practiced in a powerline communication system having three or more masters and slaves.

Also, an equally-distributed mode in which priority is not set may beprovided. In this case, a communication system which can be set to be amaster is provided, and the set master may temporally equally select acommunication system which is permitted to communicate, for example.

A method for communicating a command is not limited to theabove-described method and may be, for example, a method of using abroadband signal similar to that of a communication modem. In this case,synchronization may be established by transmitting and receiving apreamble or a synchronization flag without depending on the AC mainscycle, thereby making it possible to obtain a similar effect.

Also in a compatible system in which a coexistence controller is usedbetween a communication system having a coexistence controller and oneor more other communication systems, the mechanism of a coexistencecontrol between a master and a slave according to the present inventioncan be applied. A more specific description will be hereinafter givenwith reference to FIGS. 10 to 12.

In FIG. 10, communication systems A to C have upward compatibility witheach other. Here, for example, it is considered that, when thecommunication systems B and C can receive and decipher a beacontransmitted by the communication system A, the communication system Aindicates transmission timing of the communication systems B and C usingthe beacon. In this configuration, all the communication systems A to Cmay be of the QoS type or any of them may be of the best-effort type.Here, the QoS type communication system needs means for informing thecommunication system A of a band or a time required to guarantee QoS, inaddition to beacon reception. In the case of communication systemscompatible with each other, the informing means is considered to beeasily obtained. It is considered that, when a group of thesecommunication systems compatible with each other are a group of masters,one or a plurality of communication systems which are not compatiblewith the master group are a group of slaves. In this case, the presentinvention can be similarly applied.

An example of signal transmission and reception in the above-describedcase is illustrated in FIG. 11. All the communication systems A to C canreceive and decipher a beacon transmitted by the QoS controller of thecommunication system A, and perform transmission for the respectiveallocated time in accordance with the schedule. In the QoS typecommunication system B, the QoS controller thereof may transmit a beaconwhich describes a transmission time of a modem group belonging to thecommunication system B, at the beginning of the allocated time. Also, inthe best-effort type communication system C, a modem group belonging tothe communication system C may perform transmission while confirming afree channel, in allocated slots, in accordance with a CSMA accesscontrol method. By using the present invention after these compatiblecommunication systems A to C spend a required time, a communicationsystem which is not compatible with the communication systems A to Cperforms transmission as a slave.

Further, when the slave group has a function of receiving anddeciphering beacons transmitted by the master group, the master groupcan inform of a use time of the slave group in the schedule of thebeacon according to the present invention as illustrated in FIG. 12,thereby obtaining a similar effect. In this case, the communicationsystem B and a communication system D is different from each other inthe following point. The communication system B has means for conveyinga QoS parameter, such as a band, a transmission time or the like, whichis required to guarantee QoS, to the communication system A. Thecommunication system D which is originally not compatible with thecommunication system A has a function of receiving and deciphering abeacon, but does not have means for conveying the QoS parameter to thecommunication system A.

Second Embodiment

FIG. 13 is a diagram illustrating a configuration of a power linecommunication system according to a second embodiment of the presentinvention. In the power line communication system of the secondembodiment of FIG. 13, a QoS type communication system A and abest-effort type communication system B are connected to each other viaa power line. The communication system A comprises a power linecommunication control modem 101 including a power line communicationmodem 102, a QoS controller 103 and a coexistence controller 304, and aplurality of power line communication modems 102. The communicationsystem B comprises a power line communication control modem 201including a power line communication modem 202 and a coexistencecontroller 404, and a plurality of power line communication modems 202.

As can be seen from comparison of FIG. 1 and FIG. 13, the communicationsystem A of the second embodiment further comprises a state informationinterpreter 301 and a state information generator 302, and thecommunication system B further comprises a state information interpreter401 and a state information generator 402, as compared to those of thefirst embodiment. Other parts are similar to those described in thefirst embodiment, and therefore, are referenced with the same referencenumerals and will not be described.

FIG. 14 is a diagram illustrating an exemplary definition of signals,commands and states transmitted and received by the coexistencecontrollers 304 and 404. The coexistence controllers 304 and 404 alsouse a zero-crossing point of AC mains as a time slot reference for areason similar to that described regarding the coexistence controllers104 and 204. In the present invention, a coexistence signal is used inwhich, using a zero-crossing point of AC mains as a reference, a firstconstant period of time is a slot H1, the following constant periods oftime are slots H2 to H4, and the further following constant periods oftime are slots J1 and J2.

The slots H1 to H4 correspond to communication slots S1 to S4 obtainedby subdividing communication slot basic units which are basic units ofcoexistence due to TDM (Time Division Multiplex), and are each definedto represent a used state of the time slot using one bit. For example,bit “1” indicates that the time slot is used, and bit “0” indicates thatthe time slot is unused. In power line communication systems whichcoexist due to TDM, the whole or a part of the communication slots S1 toS4 are used to perform communication. In a normal state, thecommunication systems successively perform communication by usingpredetermined slots without collision with each other. Combinations ofbits set in the slots J1 and J2 define the following three controlcommands. Note that these control commands are only for illustrativepurposes, and can be arbitrarily set in other ways.

[J1, J2]=[0, 0]: no request

-   -   [1, 0]: low-priority communication slot request command    -   [1, 1]: high-priority communication slot request command

FIG. 15 is a flowchart illustrating operations of the coexistencecontrollers 304 and 404 when requesting a communication slot.

The coexistence controller 304 or 404 of a communication system whichrequests a communication slot transmits a request command, i.e., acoexistence signal in which bit “1” is set in the slot J1 (step S1501).To prevent malfunction, a transmission side may transmit a coexistencesignal consecutively a specified number of times or more, and a receiverside may interpret that there are a specified number or more of times ofsignal transmission in which a coexistence signal has been received. Ina system having a high priority, bit “1” is set in the slot J2 as well.

Next, the coexistence controller 304 or 404 of a communication systemwhich requests a communication slot confirms a free slot having bit “0”among the slots H1 to H4 (steps S1502 and S1503), and uses thecommunication slots S1 to S4 corresponding to the free slot to startdata communication (step S1504) If there is no free slot, thecoexistence controller 304 or 404 gives up communication. Note that itcan be arbitrarily set how many slots one communication system cansecure simultaneously. For example, when a maximum of two communicationslots can be simultaneously secured, it is forbidden to simultaneouslysecure three or more communication slots. In this case, however, a totalof three or more communication slots may be occupied by repeating aresource request procedure. However, signals in the next slots J1 and J2can be only transmitted a predetermined time interval after securing aresource (step S1505).

FIG. 16 is a flowchart illustrating an operation when the coexistencecontrollers 304 and 404 which are using a communication slot detectssignals in the slots J1 and J2.

A communication system invariably confirms a signal which is transmittedand received by the coexistence controller 304 or 404 and is passed on apower line in constant cycles (i.e., a command and a state signal),using a zero-crossing point of AC mains as a reference. Thereafter, whena signal (bit=1) in the slot J1 is received, the operation of FIG. 16 isstarted. Note that, assuming that it is previously determined that acommunication system which requests a communication slot transmitssignals in the slots J1 and J2 a predetermined number of times, if theoperation of FIG. 16 is started when the signals have been received aplurality of times, a control having less malfunction can be achieved.

In FIG. 16, the communication system which has received the signal inthe slot J1, determines whether or not there is also a signal (bit=1) inthe slot J2 (step S1601). When determining that there is also a signalin the slot J2, the communication system determines that a communicationsystem having a high priority requests participation. Thereafter, thecommunication system determines its own priority (step S1602) andconfirms a currently used communication slot (steps S1603 and S1606).

When a communication system has a high priority and uses three or morecommunication slots, only two communication slots can be continued touse, and the other communication slots are freed (step S1604). On theother hand, when a communication system has a high priority and uses twoor less communication slots, the currently used communication slots arecontinued to use, or a communication slot, if any, is freed (stepS1605).

When a communication system has a low priority and uses three or morecommunication slots, two or more communication slots are freed (stepS1607). On the other hand, when a communication system has a lowpriority and two or less communication slots, all the currently usedcommunication slots are freed (step S1608).

When a communication system determines that there is not a signal in theslot J2, the communication system determines that a communication systemwhich has a bit set in the slot J1 has a low priority. Thereafter, thecommunication system determines its own priority (step S1609). When acommunication system determines that its own priority is high, thecommunication system continues to use a currently used communicationslot, or frees a communication slot to be freed, if any (step S1610). Onthe other hand, when a communication system determines that its ownpriority is low, the communication system frees half of currently usedcommunication slots (step S1611).

As described above, according to the power line communication system ofthe second embodiment of the present invention, a communication systemhaving a high priority uses a minimum number of communication slotsrequired to secure QoS of the system, and if there is a remainingcommunication slot, allocates the remaining slot to a communicationsystem having a low priority. Note that, if two communication'systemshave the same priority, halves of communication slots may be used forthe respective communication slots. For example, it is considered that,if a transmission distance with respect to a power line of a neighboringhome in an apartment house or the like, so that power line communicationmodems interfere with each other, a user in each home sets the same highpriority. Therefore, the present invention is useful in such a case.

Note that the whole or a part of the functional blocks constituting thecoexistence controller described in the first and second embodiments maybe typically implemented as an integrated circuit (LSI: LSI is be calledIC, system LSI, super LSI, ultra LSI or the like, depending on thepackaging density). Each functional block may be separately mounted onone chip, or the whole or a part of the functional blocks may be mountedon one chip.

The integrated circuit is not limited to LSI. The integrated circuit maybe achieved by a dedicated circuit or a general-purpose processor.Further, an FPGA (Field Programmable Gate Array) which can be programmedafter LSI production or a reconfigurable processor in which connectionor settings of circuit cells in LSI can be reconfigured, may be used.

Furthermore, if an integrated circuit technology which replaces LSI isdeveloped by an advance in the semiconductor technology or the advent ofother technologies derived therefrom, the functional blocks may bepackaged using such technologies. A biotechnology may be applicable.

Note that the functions of the power line communication systems of thefirst and second embodiments can be each implemented by causing a CPU tointerpret and execute predetermined program data capable of executingthe above-described procedure, the program being stored in a storageapparatus (a ROM, a RAM, a hard disk, etc.). In this case, the programdata may be stored into the storage apparatus via a recording medium, ormay be executed directly from the recording medium. The recording mediumrefers to a semiconductor memory, such as a ROM, a RAM, a flash memoryor the like; a magnetic disk memory, such as a flexible disk, a harddisk or the like; an optical disc, such as a CD-ROM, a DVD, a BD or thelike; a memory card; or the like. The recording medium is a conceptincluding a communication medium, such as a telephone line, a transferline or the like.

The in-home communication apparatus including the present invention maybe in the form of an adaptor which converts a signal interface, such asEthernet interface, IEEE1394 interface, USB interface or the like, intointerface for power line communication, and thereby, can be connected tomultimedia apparatuses, such as a personal computer, a DVD recorder, adigital television, a home system server and the like, which have signalinterface. Thereby, a network system which transmits digital data, suchas multimedia data or the like, via a power line as a medium with highspeed, can be constructed. As a result, a power line which is alreadyprovided in homes, offices and the like can be directly used as anetwork line without newly introducing a network cable, such as aconventional wired LAN. Therefore, the present invention is considerablyuseful in terms of cost and ease of installation.

The functions of the present invention may be incorporated intomultimedia apparatuses in the future. Thereby, data transfer can beachieved between apparatuses via a power supply cable of the multimediaapparatus. In this case, an adaptor, an Ethernet cable, an IEEE1394cable, a USB cable and the like are not required, thereby simplifyingwiring. Also, the high-speed power line transmission system of thepresent invention can be connected via a rooter to the Internet, or viaa hub or the like to a wireless LAN or a conventional wired cable LAN,thereby extending a LAN system in which the high-speed power linetransmission system of the present invention is used without anyproblem.

Communication data transferred via a power line by power linetransmission may be intercepted by an apparatus directly connected tothe power line, but is free from an eavesdrop problem with wireless LAN.Therefore, the power line transmission scheme is effective for dataprotection in terms of security. Further, data transferred on a powerline may be protected by IPSec of an IP protocol, encryption of thecontents themselves, other DRM schemes or the like.

As compared to conventional power line communication, high-quality AVcontent transmission on a power line can be achieved by using acopyright protection function employing the above-described encryptionof contents or efficient communication media (an effect of the presentinvention), and further implementing a QoS function.

While the invention has been described in detail, the foregoingdescription is in all aspects illustrative and not restrictive. It isunderstood that numerous other modifications and variations can bedevised without departing from the scope of the invention.

1. A communication apparatus belonging to a first communication system,among a plurality of communication systems which coexist on a samecommunication medium by time division communication using communicationslots, the communications apparatus comprising: a controller formanaging the communication slots necessary for the first communicationsystem; a communication manager for managing transmission times of datacommunication performed by all communication modems in the plurality ofcommunication systems in cooperation with the controller, and thecommunication slots used for data communication; a command generator forgenerating a request command which requests use of a communication slotnecessary for the first communication system, in accordance with aninstruction of the communication manager; a transmitter for transmittingthe request command generated by the command generator, to a secondcommunication system among the plurality of communication systems; areceiver for receiving the request command representing a request foruse of the communication slot, from a second communication apparatusbelonging to the second communication system among the plurality ofcommunication systems; and a communication manager for freeing at leasthalf of the communication slots, when the request command is receivedfrom the second communication apparatus in a state where an entirety ofthe communication slots which can be used are used.
 2. The communicationapparatus according to claim 1, further comprising a state informationgenerator for generating information about usage state of thecommunication slot to be used for data communication with the secondcommunication apparatus, wherein the transmitter transmits, to thesecond communication apparatus, the information about the usage state ofthe communication slot, which has been generated by the stateinformation generator.
 3. A communication apparatus belonging to a firstcommunication system, among a plurality of communication systems whichcoexist on a same communication medium by time division communicationusing communication slots, the communication apparatus comprising: areceiver for receiving, from a second communication apparatus belongingto a second communication system among the plurality of communicationsystems, a request command which represents a request for use of acommunication slot and which includes information about a priority ofthe second communication system; and a communication manager forcomparing a priority of the communication apparatus including thecommunication manager, with a priority, of the second communicationsystem, included in the request command which has been received by thereceiver from the second communication apparatus, and determining anumber of the communication slots to be freed among the communicationslots being used, to free the communication slots in accordance with thedetermined number of the communication slots, wherein the communicationmanager frees half of the communication slots among the communicationslots being used, when the priority, of the second communication system,included in the request command having been received from the secondcommunication apparatus is higher than the priority of the communicationapparatus including the communication manager.
 4. The communicationapparatus according to claim 3, wherein: the receiver receives, from thesecond communication apparatus, information about a usage state of thecommunication slot used for data communication by the secondcommunication apparatus, and the communication manager confirms theusage state of the communication slot based on the information about theusage state received by the receiver after a predetermined constant timehas elapsed since the determined number of the communication slots arefreed, and uses a free communication slot.
 5. A communication apparatusbelonging to a first communication system, among a plurality ofcommunication systems which coexist on a same communication medium bytime division communication using communication slots, the communicationapparatus comprising: a receiver for receiving, from a secondcommunication apparatus belonging to a second communication system amongthe plurality of communication systems, a request command whichrepresents a request for use of a communication slot and which includesinformation about a priority of the second communication system; and acommunication manager for comparing a priority of the communicationapparatus including the communication manager, with a priority, of thesecond communication system, included in the request command which hasbeen received by the receiver from the second communication apparatus,and determining a number of the communication slots to be freed amongthe communication slots being used, to free the communication slots inaccordance with the determined number of the communication slots,wherein the communication manager frees a quarter of the communicationslots among the communication slots being used, when the priority, ofthe second communication system, included in the request command havingbeen received from the second communication apparatus is lower than thepriority of the communication apparatus including the communicationmanager.
 6. The communication apparatus according to claim 5, wherein:the receiver receives, from the second communication apparatus,information about a usage state of the communication slot used for datacommunication by the second communication apparatus, and thecommunication manager confirms the usage state of the communication slotbased on the information about the usage state received by the receiverafter a predetermined constant time has elapsed since the determinednumber of the communication slots are freed, and uses a freecommunication slot.